Quenching bath



Patented Feb. 2, 1926.

UNITED STATES.

PATENT OFFICE.

WILLIAM J. MEBTEN, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB 'IO WESTING-HOUSE ELECTRIC A: IANUIACTURING COMPANY, A CORPORATION 01' PINNSYL-VANIA.

= QUENCHING BATH.

No Drawing.

To all whom it may concern:

Be it known that I, WILLIAM J. MERTEN, a citizen of the United States,and a resident of Pittsburgh, in the count of Allegheny and State ofPennsylvania, ave invented a new and useful Improvement in QuenchingBaths, of which the following is a specification.

My invention relates to a composition of matter and more specifically toa quenching bath for use in the heat treatment of steel.

It is among the objects of my invention to provide a quenching bath thatwill quickly and uniformly cool the heated specimen in such manner thatsoft spots or hairlike cracks are not formed in the steel.

It is the practice in making objects of steel, such as tools, to forgethe material into the desired shape and then to harden the steel byheating to the desired temperature and quenching. A fused salt bath isone of the commonly used means for heating the steel, as the temperatureof the same is readily controlled and because the steel is protectedfrom oxidation and decarbonization during heating. Baths ordinarily usedfor quenching are either water, lime, oil or a solution of sodiumchloride in water and sulphuric acid. When any of the above bathsareused for quenching after having been heated in fused salt mixtures,the steel develops hair-like cracks and soft spots in the surfacethereof.

Heretofore, it has been believed that such defects were caused either bythe lack of unformity in the composition of the steel or by reason ofuneven heating and decarburization of the steel. I have discovered thatthe defects are results of the uneven cooling when the steel isquenched.

lVhen steel is quenched in the baths hitherto used, the steel isprotected by a film of oxide or gas or other heat non-conductingmaterial, so that certain small areas in the specimen are cooled lessrapidly than the rest of the specimen For example, a dense troostiticstructure is formed in one small area and a less dense martinsiticstructure occurs in the immediate adjoining area. Therefore, enormousinternal stresses are developed in the steel. The excessive stress inthe less dense martinsitic area is conducive to a change of structure tothe more stable and more dense troostitic condition Application filedMay 4, 1926. Serial No. 28,014.

and, as a result, hair-like cracks and checks occur-in the surface ofthe steel. A finish grinding operation, which roduces local heating, isparticularly likely to develop such defects. The development of softspots 111 the steel is also caused by the lack of uniformity inconducting the heat awa from the steel in the quenching bath. T e lackof uniformity in conducting heat from the steel is the result of filmsof gas and surface oxides of low heat conductivity and also of surfacefilms of salts or highly concentrated solutions thereof having low heatconductivlty. My invention provides a which instantly dissolves auenching bath it the steel ering salt on and prevents the formation ofvapor, gas or oxide films of low heat conductivity. When the steel isimmersed in the bath it is quickly and uniformly cooled and theresultlng surfaceis free from soft spots and hair-like cracks.

I provide a bath containing a combination of constituents which reactwith the vapors and non-conducting films on the surface of the steel todissolve, eliminate and prevent the formation of heat insulators ornon-conductors as fast as they are formed. I prefer a bath of theapproximate composition: water 48%, sodium chloride 24%, lime 16%,sodium cyanide 12%.

In use, the bath is agitated to keep the lime in suspension.

the surface occurs on the steel, and the steel retains its originallustre.

Although I have described a specific bath embodying my invention, I donot WlSll to be limited thereto, as the roportions of the severalconstituent may modified. For

.cxample, I vary the proportion of lime and When steel is quenched inthis bath, not even a slight oxidation of an alkali metal cyanide and anoxide of an alkalineparth metal.

2. A quenching bath which comprises an aqueous solution of a mixture ofalkali metal chlorides, a mixture of alkali metal cyanides and oxides ofalkaline earthmetals.

3. A quenching bath which com rises an aqueous solution of a metal choride, a

metal cyanide and a metal oxide. 7

4. A quenching bath WlllCh comprises an aqueous solution of sodiumchloride, so- (lium cyanide and lime.

5 A quenching bath which comprises about 24% sodium chloride, 12% sodiumcyanide, 16% lime I 6. A quenchin bath which comprises 15 to 24 o of anal ali chloride, 5 to 20% of an al ah c anide, 5 to 20% of an alkalineearth meta oxide and the remainder water.

In testimonywhereof, I have hereunto l0 iiggcribed my name this 29th dayof April,

. WILLIAM J. MERTEN.

and the remainder Water. ll

